Solid state display composed of an array of discrete elements having movable surfaces



April 2, 1968 D. s. KUSHNER ET AL 3,376,092 CRETE SOLID STATE DISPLAY COMPOSED OF AN ARRAY OF DIS ELEMENTS HAVING MOVABLE SURFACES 7 Sheets-Sheet l Filed Feb. 13, 1964 pr 2, 1968 D. s. KUSHNER ETAL 3,376,092

AN ARRAY OF DISCRETE ELEMENTS HAVING MOVABLE SURFACES SOLID STATE DISPLAY COMPOSED OF Filed Feb. l5, 1964 aj/ w V flfm/mane? Q @a kf@ a 6,9

gf 1r 3,376,092 N ARRAY 0F DISCRETE SUHFACES Apr 2, 1968 D. s. KUsHNr-:R ET AL SOLID STATE DISPLAY COMPOSED OF A ELEMENTS HAVING MOVABLE Filed Feb. 13, 1964 '7 Sheets-Sheet 3 Apu-i3 2, 968 D. .KUSHNER ETAL 376 92 SOLID STAT ISP COMPOSED OF AN ARRAY OF' DISCRETE E MENTS HAVING MOVABLE SURFACES Filed Feb. 13, 1964 '7 Sheets-Sheet 4 April 2, 1968 Filed Feb. 13, 1964 ELEMENTS HAVING MOVABL D s KU NER ETAL 3,376,092

SOLID STATE DISP'LM: com SED OF AN ARRAY DISCRETE E sURFAc 7 Sheets-Sheet 5 sr/Mzf/wr, 5,155,555@ ifa/@few D. S. KUSHNER ET AL SPL Apri 2, 1968 3,3 76,092 AY OF DISCRETE ACES SOLID STATE DI AY COMPOSED OF AN ARR ELEMENTS HAVING MOVABLE SURF Filed Feb. l5. 1964 '7 Sheets-Sheet G PI 2, 1968 D. s. KUSHNER ETAL 3,3 76,092 ISCRETE SOLID STATE DISPLAY COMPOSED OF AN ARRAY OF D ELEMENTS HAVING MOVABLE SURFACES 7 Sheets-Sheet '7 Filed Feb. 13, 1964 INN. E

NNNNNN United States Patent O SOLID STATE DISIJLAY CQMPOSED OF AN AR- RAY F DISCRETE ELEMENTS HAVING MOV- ABLE SURFACES David S. Kushner, @ld Bethpage, and Elliott H. Kahn,

Brooklyn, NSY., assignors to Kollsman Instrument Corporation, Elmhurst, NX., a corporation of New York Filed Feb. I3, 1964, Ser. No. 344,720 9 Claims. (Cl. S50-285) ABSTRACT F THE DISCLOSURE A display composed of a matrix of individually movable members having surfaces movable from one plane to another in order to modify the illumination observed at their respective discrete positions. The individual members are piezoelectric or magnetostrictive elements which are individually electrically extended and contracted to modify the position of their individual illumination controlling surfaces.

This invention relates to display apparatus and more specifically relates to a novel display structure wherein the reflectance of a reflecting body is controlled over the surface area of the body through frustration of total internal reflectance.

It is well known that the total internal reflectance of a glass to air surface can be partially or completely destroyed (or frustrated) by bringing a second glass body adjacent to the reflecting surface. The closer the body is brought, the less reflectance will be obtained from the glass to air boundary.

The principle of the present invention is to provide a novel mosaic of frustrator elements adjacent a reflecting surface wherein elements of the mosaic are selectively moved toward or away from the surface and thus control the amount of reflection obtained from the surface. In this manner, and by properly and selectively permitting and destroying reflection for discrete areas of the reflecting surface, any desired pattern of the reflected light may be selected. Thus, the pattern of a numeral, or the like, can be selected by the mosaic to be totally reflected toward a screen or similar display.

The mosaic may be formed in any desired manner as by discrete elements of a larger surface or by longitudinal sections of a large surface. They may be moved by any suitable mechanism as by forming the mosaic elements themselves of a piezoelectric material or a magnetostrictive material having polished end surfaces. Alternatively, piezoelectric or magnetostrictive bodies may be used merely to drive separate mosaic elements. Generally, it is possible to use any type of driving mechanism which may or may not have a memory such as characterizes many well-known ferroelectric and ferromagnetic materials.

It will be apparent that the use of this concept will permit the construction of displays having few moving parts or mechanical linkages and which are small in size. Moreover, the devices are extremely simple in construction and will be extremely reliable in operation.

Accordingly, the primary object of this invention is to provide a novel display device using the phenomenon of frustration of total internal reflection.

Another object of this invention is to provide a novel display device using no mechanical linkages.

Yet another object of this invention is to provide a novel solid state type display device.

A further object of this invention is to provide a novel display mechanism which has in inherent memory capability.

A further object of this invention is to provide a novel display device which is extremely resistant to and is unaffected by shock and vibration.

Still another object of this invention is to provide a novel solid state indicator device which is small in size.

These and other objects of this invention will become apparent from the following description of the drawings in which:

FIGURE l is a schematic diagram of an optical system for illustrating the concept of frustration of total reflection.

FIGURE 2 is a chart illustrating the relationship between reflectance or transmittance as a function of the spacing of the frustrator element of FIGURE l from the reflecting boundary.

FIGURE 3 is a perspective view which illustrates one manner in which a magnetostrictive matrix of frustrator elements can be formed.

FIGURE 4 illustrates a further form of a magnetostrictive matrix plate in perspective view.

FIGURE 5 illustrates the manner in which conductive lines may be formed on one surface of the plate of FIG- URE 4.

FIGURE 6 illustrates the manner in which conductive lines are formed on both surfaces of the plate of FIG- URE 4.

FIGURE 7 shows a perspective View of a second type of magnetostrictive frustrator mosaic.

FIGURE 7a illustrates the manner in which a single longitudinally extending magnetostrictive element or slab can be formed.

FIGURE 7b illustrates the manner in which the elements of FIGURE 7a are arranged with respect to one another in a matrix of elements.

FIGURE 8 illustrates the type mosaic shown in FIG- URE 7 which uses piezoelectric elements.

FIGURE 8a illustrates the manner in which longitudinally extending piezoelectric elements or slabs can be arranged in an array.

FIGURE 9 illustrates the manner in which any of the mosaics of FIGURES 7, 7b, 8 and 8a may be arranged with respect to a reflecting surface.

FIGURE l0 illustrates the manner in which the arrangement of FIGURE 9 can be used in a projection device.

FIGURE ll is a perspective view of an altimeter cut through its center to illustrate the manner in which a conical ring-shaped frustrator array can be used for a curved scale instrument.

FIGURE l2 shows a perspective view of an instrument cut through the middle and illustrates the manner in which an array may be used for a straight scale instrument.

FIGURE 13 is an exploded perspective view of the frustrator array structure of FIGURE 12.

FIGURE 14 schematically illustrates a control circuitry for driving the piezoelectric array of elements of FIG- URES l2 and 13.

Referring first to FIGURE l and for purposes of describing the phenomenon of frustrated total internal reflection. We have illustrated a glass prism 3h having an index of refration n1. A suitable light source of collimated light (not shown) then introduces light, illustrated by rays 31 and 32, into one surface of prism 36. These rays then strike the lower surface 33 of prism 30 which is a boundary between the prism index refraction nl and the index of refraction n2 of the medium external prism 30. This light strikes boundary 33 at an angle greater than the critical angle so that the light is normally totally internally reflected as shown.

It is well known that this total internal reflection can be destroyed (or frustrated) by bringing a second medium very close to the totally reflecting interface 33. Thus in FIGUREI we have shown a body 34 having an index of refraction n3 which is spaced from boundary 33 by the distance d. The index of refraction is preferably similar but not necessarily exactly equal to n1. In general, so long as the distance d is greater than some pre-determined amount, the collimated light impinging on boundary 33 and at an angle greater than the critical angle will be totally reflected. However, as body 34 is brought close to boundary 33, a portion of the incident light on boundary 33 will be transmited through boundary 33 and the total internal reflection is spoiled. Thus by making minor changes in dimension d, it is possible to cause major changes in the transmission of light at interface 33. This is illustrated in FIGURE 2 where reflectance and transmittance at interface 33 are plotted against the distance d, divided by wave length A of the light used.

As shown in FIGURE 2, the movements of body 34 over a distance equivalent to only one wave length of the light used is sufficient to pass from virtually total transmission to virtually total reflection.

The principle of the present invention is to utilize this concept of frustration of total internal reflection for display purposes. To this end discrete areas of a display surface are provided with small movable frustrator elements which move with respect to a totally reflecting boundary surface. By suitably selecting and moving these elements toward the boundary surface, it is clear that the total reflectance in these areas will be frustrated. Alternatively, a matrix of elements may be positioned to normally frustrate internal total reflection with the individual elements being movable to a non-frustrated position.

A typical arrangement of frustrator elements is schematically illustrated in FIGURE 3. More specifically, FIGURE 3 illustrates a support body 40 which has a plurality of magnetostrictive elements such as magnetostrictve element 41 through 46 mounted thereon.

Elements 41 through 46 are of any suitable magnetostrictive material and are characterized in being constricted in length in response to any axially directed magnetic field. The top and free surfaces of elements 41 through 46 are polished and are coplanar with one another, and are located adjacent to a totally reflecting boundary which will be placed atop elements 41 through 46. l

The top surfaces of elements 41 through 46 would then be placed against (or within 1A: wave length of) the total .reflecting boundary. In this condition, the reflecting 'boundary will be virtually non-reflecting, at least in the region of members 41 through 46, since they destroy or frustrate the total reflection normally occurring at the boundary. A suitable circuit is then provided for causing the elements 41 through 46 to constrict selectively and thereby reinstate the total reflection of the boundary areas adjacent to the area of the individual elements.

This circuit is partially illustrated in FIGURE 3 by conductors 50, 51, 52 and 53 which form a typical addressable system for selecting any of the magnetostrictive elements of the array. For example, if both conductors 50 and 52 are energized, the magnetic field of these conductors will add in element 41 and thus cause element 41 to constrict and thus move its upper surface away from the reflecting boundary. Note that the element 42 will not constrict substantially since the magnetic field due solely to conductor 50 will be insufficient to cause a substantial restriction operation.

The individual rods 41 through 46 may be made of nickel which has a magnetostrictive effect of approximately 30 parts per million. A'rod length of approximately of 1A inch would be sufficient to effect a displacement of the rod end of about 1A wave length for light in the visible range. It is to be noted that if the material used is driven in the linear region of its magnetostrictive characteristic, the selected rod, at the intersection of an energized row and column, which receives twice the magnetic flux of the others, will constrict by twice the amount of the others. The constriction of all of the unselected elements, however, is undesirable and constitutes noise on the display. This effect may be reduced, however, by driving the magnetostrictive elements in the non-linear region of the reflectance curve of FIGURE 2. This noise characteristic can be further reduced through the use of non-linear magnetostrictive materials such as many of the well-known magnetostrictive ferrites.

While FIGURE 3 illustrates discrete magnetostrictive elements, FIGURE 4 illustrates an arrangement utilizing a single sheet 60 of magnetostrictive material which is used as a subsurface matrix plate. The drive lines for controlling the discrete area operation of plate 60 are the conductors 61 through 65 on the upper surface of plate 60 and which are deposited on the plate through any suitable plating type technique. FIGURE 5 shows a cross-section of the portion of plate 60 which receives conductor 6l.

A second set of conductors may then be plated on the bottom surface of sheet 60 and includes conductors 66 through 70, as illustrated in FIGURE 6. Note that current input of the aligned conductors of FIGURE 6 is in the same `direction so that their magnetic field is additive. The use of the double current flow arrangement of FIG- URE 6 causes the lines of magnetic force to extend completely through body 60 rather than just through the surface thereof as illustrated in FIGURE 5.

In operation, the magnetic lines of force through the body 60 and particularly at those regions of intersecting lines and columns will tend to cause bumps or form depressions in the surface of the material. This, of course, can be used to control the internal reflectance of an adjacently positioned total internal reflecting boundary.

As was the case of FIGURE 3, a non-linear magnetostrictve material can be used for plate 60 to suppress the effects along the energized row and column lines, while allowing an appreciable dimensional change only at the intersection of a selected row and column.

A further form of magnetostrictive frustrator mosaic is shown in the perspective view of FIGURE 7. More specifically, FIGURE 7 illustrates a support frame 80 which may be of any suitable rigid material which receives a plurality of pillar elements such as elements 81, 82 and 83. A suitable bonding cement 84 secures these elements to the frame 80. Each of the pillar elements may be formed of a suitable ferrite such as a lead zirconium-titanate ceramic which is molded to have internal slots such as slots 85 and 86 which extend completely through pillars 81 and 82. The elements further have extending flange heads at their top and bott-om such as upper flange heads 87 and 88 shown for elements 82 and 83 respectively. The flange head arrangement is used to define a channel 89 which extends completely along the junction between adjacent rows of elements. The totally internal reflecting surface is then located atop frame and the upper ends of the pillars such as pillars 81 through 83.

After the assembly of the mosaic elements, the complete upper face is ground flat to a tolerance of the order of several thousandths of an inch. Since the inherent grains of the ferrite or ferroelectric ceramic material does not permit it to be polished to a suitable degree of smoothness (several millionths of an inch), the entire mosaic surface is coated with a material that is capable of taking an optically flat finish. By way of example, a nickel-nickel phosphor known by the name, Kanigen, which is extensively used in optically polishable plating for beryllium mirrors may be used according to known techniques.

Alternatively, a glass frit or powdered glass may be deposited on the surface and fused in an oven, and thereafter polished. Whichever technique is used for the coating operation, the mosaic surface is ground flat to a precision of approximately 1/10 of a wave length. This permits contact between the frustrator and the reflecting surface to be within the order of 1/10 of a wave length where the reflecting surface is absolutely flat, This match may be improved by polishing the frustrator surface to match the contour of the totally reflecting surface.

In order to selectively energize individual elements of the array, a first set of electrical conductors such as conductors 90 and 91 enter the frame 80 and are wound about the various pillars in the manner shown. These can be considered to be the word lines of the array. A second set of conductors such as conductors 92 through 96 which carry current in alternate direction then pass through channels such as channel 85 and form the bit line.

The operation of the system will clearly be such that -only that pillar at the intersection of an energized word line and bit line will be Substantially deflected in a compressive direction'. Thus total internal rellection at the area adjacent this withdrawn element will be eliminated so that there can be a total reflection at that area.

It will be recalled that the surface coating on the various pillars was laid down as a continuous sheet. How` ever, this coating is extremely thin and the magnetostrictive forces are relatively high. Thus the material will be caused to flex in a manner which closely approximates that which would be obtained if the mosaic elements were separated. However, where there is too great a loss due to the flexing operation, it is clearly possible to individually coat the tops of the mosaic element before their assembly in the array, or to coat them with suitable separators in position.

While the array of magnetostrictive elements is shown in FIGURE 7 as formed of rows and columns of pillar elements, it will be understood that the elements can be formed `of parallel elongated members, or slabs, stacked directly atop one another. By way of example, FIGURE 7a illustrates an elongated magnetostrictive element which is a slotted slab of a suitable magnetostrictive material.

A llat conductor 101 which has an insulation film coating 102 passes through slotted opening in member 100, whereby current flow, indicated by arrow 193, will cause a magnetic field in the direction of the dotted line arrows. The direction of magnetostrictive motion is a compressive motion indicated, for example, by arrows 104a and 104i). The slabs, such as slab 100 of FIGURE 7a, are then assembled in the array illustrated in FIGURE 7b where each of the slabs is secured to a suitable base, such as base 105, as by a suitable bonding cement 106. The upper polished face of each of the elements 100, which are suitably polished in a manner discussed, for example, for` the elements of FIGURE 7 are then mounted in close,

proximity to a reflecting surface in a manner similar to that discussed for the array of FIGURE 7.

In the arrays of FIGURES 7 and 7b, magnetostriction is dependent only upon the magnitude of themagnetic flux and is independent of its direction. Therefore, both legs of each of the elements will contract by equal amounts, thus shortening the energized elements, It will' be noted that each individual element provides a closed path for magnetic flux so that the flux carried by one element has no effect upon its neighbors.

While the foregoing embodiments have illustrated the formation of an array of magnetostrictive elements, it is also possible to use piezoelectric elements. FIGURE 8 illustrates one manner in which the array may be formed of piezoelectric elements in a manner analogous to that of FIGURE '7. Thus, in FIGURE 8 a plurality of piezoelectric elements such as elements 110, 111, 112 and 113 are provided in the manner shown in FIGURE 7 for elements 81, 82 and 83. The upper surfaces of elements 110 through 113 are suitably polished as previously in dicated and the elements are each mounted within the frame 80 by the bonding cement S4. Each of the individual elements are formed of any suitable piezoelectric material such as polarized lead zirconium-titanate ceramic,

or the like, and are provided with opposing electrodes,y

6 such as the opposing electrodes 114 and 115 for element 112 and electrodes 116 and 117 for element 110.

One of the electrodes of each of the elements, such as electrodes 115 and 117 are elongated and bent around the bottom of their respective members so that they can make contact with conductive strips, such as conductive strips 118, 119 and 120 which serve as the Word line for the array. The bit lines are formed by insulating sheet members 121, 122 and 123 which extend perpendic ular to word lines 118 through 120 and are conductively coated `on one surface so as to be electrically connected to the other electrode of the various elements. For example, conductor 123 is electrically engaged by surfaces 114 and 126 of elements 112 and 113 respectively.

The end result of this novel arrangement is that a bit line is electrically connected -to one electrode of each element of the array while a word line is electrically connected to the other of the elements of the array. Therefore, when there is one simultaneous energization, for example, bit line 123 and word line 118, an electrostatic iield is created between the electrodes 114 and 115, whereupon the element 112 will'contact in length thus suitably altering the reflectance in the boundary area adjacent element 112.

Clearly, the piezoelectric material of FIGURE 8a could be formed of elongated members formed in a row in the manner of FIGURE 7b as specifically shown in FIGURE 8a. Thus, in FIGURE 8a the base 105 receives slabshaped piezoelectric elements 130 through 133 which each have polished upper surfaces as previously described. Each of slabs 130 through 133 then have opposing electrodes on their large area surface such as the plated electrodes 134 and 135 for element 133. A plurality of insulating sheets having metalized coatings on both sides, such as sheets 136 through 139 are then suitably arranged and are electrically connectable to suitable control circuitry. Thus, when sheets 138 and 139 are energized, the elements 133 will be caused to deflect in a manner similar to that of FIGURE 7b.

The manner in which the array is mounted, whether it is formed in the manner shown in FIGURES 7, 7a, 7b, 8 or 8a, is illustrated in FIGURE 9 where the frustrator mosaic is indicated by numeral 150, which has mosaic elements therein as indicated by the dotted lines. The upper polished surfaces of the various elements of mosaic 150 are then placed immediately adjacent the reflecting surface 151 of a prism 152.

The surface area of surface 151 is co-extensive with the upper surface area of mosaic 150. Thus, if one or more elements of the mosaic are distorted from their normal position, the incident light indicated by arrows 153,at that particular surface area will not be included in the reflected image of the surface of mosaic 150 indicated by arrows 154.

This novel concept will now have a great number of possible applications. By way of example, FIGURE l0 illustrates the manner in which the concept can be used for projection. Thus in FIGURE l0, the mosaic 150 and prism 152 are assembled with a suitable light source which provides a collimated beam of incident light indicated by arrow 153.

A display screen 160 is then provided which may be a large area display screen which physically displays the information applied to the frustrator mosaic in that the surface area of screen will either be devoid of light at a corresponding surface area to'that of the frustrator mosaic, or will only be illuminated at that selected point. For this purpose, the projector system will include oblique view correction prism 161 and a projection lens 162. This arrangement permits the reproduction on the display screen which corresponds exactly to the energization of the frustrator mosaic 150. Thus, the mosaic structure 150 permits a writing of bright increments into a normally ydark display or alternatively by writing dark increments into a normally illuminated display.

This novel arrangement may be particularly usefully applied to indicator instruments of various types. By way of example, FIGURE 11 illustrates a curved dial instrumentwhich could, for example, indicate altitude and be driven in accordance with the present invention. More specifically, the instrument of FIGURE 11 is comprised of a suitable housing 170 which has contained therein an annular prism 171 which has the increments of an indieating dial visible through front surface 172. The conical surface 173 of prism 171 then receives an annular frustrator array 174 whose inner surface is spaced from surface 173, for example, by 1/10 of a wave length. The frustrator array 173, while annular in configuration, will clearly be arranged in the manner indicated, for example, in FIGURES 7b or `8a with the elongated elements of the array lying in respective planes which pass through the axis of prism 171.

The housing 171 further contains a lamp 175 which passes light through the inner surface 176 of prism 171 and on to the reflecting surface 173 of prism 171. The surface 173 makes an angle with respect to illumination from lamp 175 which is less than the critical angle, so that there would normally be total internal reflection of this light toward and out of surface 172. This condition, however, is frustrated by the close spacing of the frustrator array 173 so that under normal conditions the scale of surface 172 is dark. If, however, one of the slabtype elements in frustrator array 173 is energized, it is removed from its closely spaced position to surface 173 so that there will be substantial reflection of light at this area. This reflection of light at the selected area will then show up on scale 72 as a bright line on a dark background.

Clearly, the circuitry which drives the frustrator array 174 will be connected to a suitable altitude measuring structure, or the like, wherein the measured altitude is suitably converted to energize the appropriate slab of the array 174.

It will be recalled that the frustrator array reflecting surface is laid down as a continuous surface coating which is flexed at the region of the energized element. By varying the thickness of this coating, it is possible to adjust the radius of flexure of the coating to provide a pointer width equal to that of several of the segments while still maintaining single segment resolution for the center of the pointen Clearly, however, the mosaic elements can be assembled with suitable separators so that only the individual coatings of the discrete mosaic segments are moved.

In the instrument of FIGURE ll, the scale markings are placed ydirectly on face 172 of prism 171. Thus the dial preferably should have separate illumination so that the scale markings can be seen.

These scale markings may also be provided by etching them directly into the reflecting surface 173 so that the etched markings will scatter and reflect the light which comes from lamp 175. Thus the scale markings will appear bright in a dark background, and separate illumination of the face of the instrument is not required.

It is also possible, of course, to have the background normally illuminated, with both numerals and pointer being formed of darkened areas in the illuminated background. In this arrangement, the frustrator array normally does not interfere with total internal reflection. However, the etched markings are filled with a darkened pigment so that the numerals are observed as dark areas while the flexure of the suitable frustrator mosaic element will destroy internal reflection at the selected point.

FIGURES l2 and 13 illustrate the manner in which the invention may be used for a straight scale type indicating instrument. Referring first to FIGURE 12, there is illustrated therein, for an altimeter, for example, a housing 180 which has a dial face 181 which has a cut-out 182 therein. A prism 183 is then mounted adjacent opening 182 while a frustrator array generally shown as array 183:1 is mounted adjacent the reflecting surface 184 of prism 183. The array 183a is best shown in FIGURE 13 as including a mounting frame 185 which receives a stack 186 of suitable dellectable stacked elements which may -be stacked in the manner illustrated in FIGURE 7b or 8a.

The reflecting surface 184 of prism 183 is mounted directly atop the upper surface of array 186 and preferably is Within 1/10 of a wave length from the surface. Two spaces 186 and 188 are then located at either end of stack 186 which is suitably cemented to the base 185 by the cement 189. The spacers 187 and 188 insure suitable spacing of the main frame 190 from the base 185. Note that prism 183 has a notch 196 adjacent its viewing surface 197 which is received by the projecting ledge 198 of frame member 190 thereby holding prism 183 in position with respect to elements 186. The upper surface of array 186 is held firmly against the reflecting surface 184 of prism 183 by pressure from springs 194, 195 and 196, which are held by retaining screws 191, 192 and 193.

A suitable light source including the lamps 200 (FIG- URE 12) and reflector 201 is then arranged to pass light through illumination windows 201 and 202 of frame member 190 and toward the reflecting surface 184 of prism 183.

The operation of the straight scale instrument device of FIGURE 12 is ybelieved clear in that the scale may normally be darkened by frustration of internal reflection from prism surface 184 due to normally close proximity of the surface of array 186i. Once, however, one of these elements is energized by suitable energizing circuitry, it will contract and thus be removed from the reflecting surface 184 to a distance great enough to permit substantial total internal reflection at that point.

Accordingly, an illuminated line will appear across the scale viewed through window 182. Note that the calibrating numerals on the scale may be applied thereto as described in FIGURE 11.

In the embodiment of FIGURES l2 and 13, good performance will result where the scale length is of the order of five inches while the array 186 includes approximately fifty piezoelectric elements per inch. In driving this type structure, it is therefore necessary to select and energize one of the 256 elements of the array for each value of input signal. This input signal may be made available in eight-bit parallel digital form, although other forms of digital and analog inputs may be applied equally well. Itis, of course, possible to design a straight-forward decoder for the eight-bit input according to any of the well-known techniques. Thus one electrode of each of the 256 elements of array 186 would be connected to a common ground bus while any one of the 256 free electrodes would be selected and energized by the output of an eight-bit decoder.

While standard selection techniques could be utilized, FIGURE 14 illustrates a signal selection circuit which reduces to a substantial degree the amount of hardware required.

In FIGURE 14 there is illustrated an eight-bit digital input which has the four high 'bit positions connected to a four-bit decoder 210 while the four lower bits are connected to a second four-bit decoder 211. The 256 piezoelectric elements of the array of FIGURES 12 and 13 are then laid out as indicated. The left-hand electrodes of each of the piezoelectric elements are then grouped in 16 groups of 16 elements. Thus the elements 1 through 16 have their left-hand electrodes Igrouped together and connected to a common -bus 212.

In a similar manner, each of the left-hand electrodes are grouped together to form a total of 16 groups of 16 elements. Each of these groups which shall, for convenience, be called A-groups then have their 16 buses connected to the four-bit decoder 210. The four-bit decoder 210 is then capable of applying -l-E volts on a selected bus of one of the 16 bases.

The right-hand electrodes of each of the piezoelectric elements are similarly grouped into 16 groups of 16 elements which are connected to respective buses of buses 214. However, in the grouping of the right-hand electrodes, which shall be called B-groups, only one element from each of the A-groups will appear in each B-'group The B-groups are then connected as illustrated to the four-bit decoder 211 which can apply a voltage of -E volts to any of the selected buses of group 214.

In operation and assuming that the selected piezoelectric elements to be energized is the fifteenth of the 256 elements, those buses in the A-group and B-group which each include element number 15 will be energized as illustrated by the heavy line whereupon a voltage of 2E will be applied to the electrodes of element 15 to cause it to constrict. Clearly any of the remaining elements can be selected in a similar manner.

It is to be noted that this grouping arrangement of FGURE 14 can lead to the existence of sneak paths where the voltage is applied across series combinations of several elements. Such sneak paths can be easily avoided by connecting a diode in conductors leading to each of the left or right-hand electrodes of each of the piezoelectric elements.

Alternatively, the effect of sneak paths may be reduced by using the non-linear characteristics of the piezoelectric material whereby the amount of motion resulting from partial excitation is negligible comparing to that resulting from full excitation.

While the circuit of FIGURE 14 is particularly applicable for use with piezoelectric elements, it will be apparent to those skilled in the art that the concepts of FIG- URE 14 can also be applied to a magnetostrictive array with suitable modification made so that a current will be passed through the selected element rather than a voltage applied across the selected element.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specic disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. An indicating device comprising a transparent body having a surface boundary plane, an illumination source positioned on one side of said surface boundary plane and illuminating said surface boundary from said one side thereof and at an angle greater than or equal to its critical angle, and a light control structure for controlling the reflection of the illumination of said illumination source from said surface boundary plane; said light control structure positioned adjacent the opposite side of said surface boundary plane and being coextensive therewith; said light control structure comprising a plurality of ind-ividual movable elements; each of said elements having elongated side surfaces; each of said elements being stacked with their said side surfaces adjacent one another to form at least one row of said individual elements; said adjacent side sections of each of said elements being mechanically separate from the adjacent side surfaces of other of said elements; each of said elements having planar upper end surfaces terminating in a common plane and defining a continuous surface adjacent and parallel to said surface boundary plane; each of said independently movable elements being movable in a direction perpendicular to said surface boundary with said plana-r end surfaces of each of said elements movable to a plane parallel to and spaced from said common plane, thereby to Inodify the internal reflection of light from said surface boundary plane; electrically conductive operating means connected to each of said independently movable elements; and operating circuit means connected to each of said electrically conductive operating means for selectively euergizing any of said independently movable elements to move said individual elements with respect to said common plane, thereby to develop a visually observable pattern on the surface of said viewing apparatus composed of a pattern of discrete areas of different light intensities.

2. The device substantially as set forth in claim 1 wherein said transparent body is a prism.

3. The device substantially as set forth in claim 1 wherein said independently movable elements have polished surfaces adjacent said surface boundary and have an index of refraction similar to the index of refraction of said transparent body.

4. The device substantially as set forth in claim 1 wherein said individual elements are each comprised of a magnetostrictive material.

5. The device substantially as set forth in claim 1 wherein said individual elements are each comprised of a piezoelectric material.

6. The device substantially as set forth in claim 1 wherein said plurality of individual elements are arranged in a matrix of continuous rows and columns for selectively controlling the reflection of incident light on said boundary at any discrete area of said boundary adjacent a respective element.

7. The device substantially as set forth in claim 1 where each of said individual elements are formed of elongated slabs stacked atop one another.

8. 'The device substantially as set forth in claim 4 which further includes control circuit means magnetically connected to each of said magnetostrictive bodies; said control circuit means being arranged for selectively energizing any of said magnetostrictive bodies.

9. The device substantially as set forth in claim 5 which further includes control circuit means electrically connected to each of said piezoelectric bodies; said control circuit means being arranged lfor selectively energizing any of said piezoelectric bodies.

References Cited UNITED STATES PATENTS 2,185,379 1/1940 Meyers et al 350-285 X 2,281,280 4/1942 Gabor 350-161 X 2,455,763 12/1948 lHarrison 350-285 X 2,565,514 8/1951 Pajes 350-285 2,997,922 8/1961 Kaprelian 350-285 3,291,554 12/1966 Price 350-285 JEWELL H. PEDERSEN, Primary Examiner. E. BAUER, W. L. SIKES, Assistant Examiners. 

